1. Field of the Invention
A first aspect of the present invention relates to the formation of a thin film, and more particularly to a technique for forming a metal barrier film at low temperature.
A second aspect of the present invention relates to a method of forming a metal film in a semiconductor device, and more particularly to a cleaning technique used prior to the formation of a metal film on a metal surface or a Si surface.
2. Description of the Related Art
<First Aspect>
CVD apparatuses and sputtering apparatuses are typically used for forming thin films on the surfaces of semiconductor substrates.
A conventional method of manufacturing a thin film is described below, using a plasma CVD method as a specific example. The reference numeral 101 in FIG. 15 shows a conventional CVD apparatus.
This CVD apparatus 101 comprises a vacuum chamber 120, with a hot plate 121 positioned above the inside bottom surface of this vacuum chamber 120, and a high frequency electrode 122 positioned near the ceiling of the vacuum chamber 120.
Lift pins 124 are inserted inside the hot plate 121, and by activating these lift pins 124, an object to be treated can be mounted on the hot plate 121. The reference numeral 102 in FIG. 15 shows an object to be treated in this mounted state. This object 102 is heated using a heater provided within the hot plate 121.
A raw material gas supply system 127 and a high frequency power supply 126 are connected to the high frequency electrode 122. Shower nozzles 123 are provided in the bottom surface of the high frequency electrode 122, and the raw material gas, which is supplied from the raw material gas supply system 127 to the high frequency electrode 122, is sprayed into the vacuum chamber 120 through these shower nozzles 123.
If a high frequency voltage is then applied to the high frequency electrode 122 using the high frequency power supply 126, plasma of a raw material gas is generated, thereby enabling a thin film to be grown on the Si or metal surface of a semiconductor substrate.
However, the film formation method described above requires the object to be heated to a high temperature, and is consequently unsuitable for current low temperature processes.
Thin film formation methods under low temperature have been disclosed, but when these methods are used in the formation of metal wiring or metal barrier films, the resistivity of the produced films is undesirably high.
Patent Reference 1: Japanese Patent Laid-Open Publication No. 2000-269163.
Furthermore, in those cases where a copper film is partially exposed on the semiconductor substrate as the object, copper oxide and residual fluorine (F) and carbon (C) components have adhered on the surface of the copper film. during previous etching steps. If a metal barrier film is formed directly onto the surface of the Cu film in this state, it is difficult to achieve ohmic contact between the metal barrier film and the Cu.
In the conventional technology for cleaning step of the surface of the Cu film, hydrogen gas is introduced into the vacuum chamber and a high frequency (such as, RF) is applied to generate plasma. Then, the excited hydrogen ions are used to remove the insulating material comprising oxides, F components, and C components from the Cu surface. The surface of the Cu film to be treated is positioned at the bottom of fine holes (via holes). In a typical conventional example, the diameter of these holes is 0.13 μm, the depth of the holes is 0.85 μm, and the aspect ratio is 5 or more.
With the high aspect ratio, even if methods having good ion directivity into holes and grooves (such as, RIE (Reactive Ion Etching)) are used, it is known that access of the hydrogen ions into the holes is retarded by charge-up of the surface of the semiconductor substrate caused by ion impact.
On the other hand, for cleaning methods that do not use plasmas, removing the oxygen from copper oxides through a hydrogen reduction reaction are also known. However, in order to ensure an efficient reduction reaction, the substrate temperature must be at least 350° C. It is not suitable to require lower process temperatures in recent years.
<Second Aspect>
For example, copper oxide and residual fluorine (F) and carbon (C) components that have adhered during previous etching steps remain on the surface of a copper film exposed on a semiconductor substrate. If a metal barrier film is directly formed onto the surface of the Cu film in this state, it is difficult to achieve ohmic contact between the barrier metal and the Cu film.
In the conventional technology, hydrogen gas ions are introduced into the vacuum chamber and a high frequency (such as, RF) is applied to generate a plasma, so that the thus formed excited hydrogen ions are used to remove the insulating material comprising oxides, F components, and C components or the like from the Cu surface during a step for cleaning the surface of the Cu film.
The advantage of this method is that the cleaning step can be conducted at a comparatively low temperature of the substrate (200 to 300° C.) Such method is suitable for the requirement of lower process temperatures for semiconductor devices in recent years.
The surface of the Cu film to be treated is positioned at the bottom of fine holes (via holes). In a typical conventional example, the diameter of these holes is 0.13 μm, the depth of the holes is 0.85 μm, and the aspect ratio is 5 or more.
With the high aspect ratio, even if methods having good ion directivity into holes and grooves (such as, RIE (Reactive Ion Etching)) are used, it is known that access ofthe hydrogen ions into the holes is retarded by charge-up of the surface of the semiconductor substrate caused by ion impact.
In order to improve the efficiency of the treatment, either the high frequency power must be further strengthened, or the plasma density must be increased. However, the former case cause shaving of the patterning shape, whereas the latter case requires the introduction of complex and expensive systems (such as, ICP (Inductively Coupled Plasma) or ECR plasma).
Alternatively, cleaning methods without using plasmas, removing the oxygen from copper oxides through a hydrogen reduction reaction are also known.
However, in order to ensure an efficient reduction reaction, the substrate temperature must be at least 350° C. Such method is not suitable for the requirement of lower process temperatures in recent years. These methods may potentially be applied to the cleaning of the bottom portions of via holes in recent aluminum wiring processes and the cleaning of the Si surface in a transistor salicide process prior to Co or Ni sputtering.
Patent Reference 1: Japanese Patent Laid-Open Publication No. 2000-323571
Patent Reference 2: Japanese Patent Laid-Open Publication No. 2000-269163